Cylindrical cushion bushing



Nov. 15, 1960 R. E. BECKER 2,960,068

CYLINDRICAL CUSHION BUSHING Filed Aug. s. 1958 l JNVENTOR.

CYLINDRICAL CUSHION BUSHING Robert E. Becker, Logansporg Ind., assignor to Logansport Machine Co., Inc., a corporation of Indiana Filed Aug. 8, 1958, Ser. No. 754,000

2 Claims. (Cl. 121-38) This invention relates to cushioning means for cylinder and reciprocating piston assemblies.

In order to prevent shock and noise at the end of a piston stroke while, maintaining maximum length of stroke,l it is desirable to cushion a piston as it approaches e v-Hader @verf This. ushgniag effect is usually @Gwinplished by having the piston tightly fitted within the cylinder so that as the piston moves forward and reaches a pre-determined distance from the cylinder cover a cushion nose extending outwardly from the cylinder piston enters the bore of a cushion bushing in the cylinder cover to block the escape of exhaust air to the atmosphere and compress the remaining air in the cylinder ahead of the piston; the compressed air then exerting a retarding or cushioning eect on the piston.

Unless some means be provided for bleeding oif the entrapped air as the piston moves toward the cylinder cover, after the cushion nose has entered the cushion bushing bore, the piston will stop before it reaches the end of its stroke and excessive strain will be put on the sealing components, including the piston rings.

Therefore the custom-ary means of employing a by-pass hole from the cylinder bore area through a regulating needle and exhausting behind the cushion bushing to the outlet port is provided to bleed oif the entrapped air letting the piston complete its full travel at a reduced Speed.

Due to wear and the close tolerances involved, it has been found that the cushion nose and/ or cushion bushing can become misaligned. Accordingly, it is a purpose of this invention toA provide a rneans for automatically aligning the nose and bushing on each piston stroke. This can be accomplished by making the outer diameter of the cushion bushing slightly smaller than the diameter of the cylinder cover bore, so that the bushing can be radially moved until it is centered on the nose. The leading edge of the nose and the edge of the bushing bore that contacts the nose are tapered to form inclined engaging surfaces which facilitate the radial movement of the bushing.

Other purposes will appear in the ensuing specification and drawings wherein:

Figure l is a sectional view of a piston and cylinder assembly in which the piston is shown approaching the cylinder cover.

Figure 2 is a sectional view of the piston and cylinder assembly of Figure l showing the piston at the end of its stroke, and

Figure 3 is a partial section on an enlarged scale of the bushing in the position of Figure 2.

Referring now to the figures, -indicates an outer housing or wall of a cylinder or the like, which is closed by a cylinder cover 12, as at 14. An C-ring seal 16 forms a seal between the cylinder and the cylinder cover.

18 indicates a bore in the cylinder 12 which may be used both `as an intake and exhaust port. The port -18 is in communication with a generally central cylinder cover bore 20. The bore 20 has been enlarged, as at 22, to receive a cushion bushing 24, which is loosely held 2,960,068 Patented Nov. 15, 1960 2 in the bore by a retaining ring or the like, shown at 26. A passage 30, formed between the bushing 24 and the cylinder cover bore 20, is sealed by an O-ring seal 28 positioned and retained in a trepanned groove in the inner face of the cushion bushing 24.

In order to provide the automatic alignment feature above described, the bushing is loosely fitted within the bore so that there is radial freedom of movement between the bushing and the cylinder cover. For examplewith a four Vinch cylinder a clearance of .005 to .010 inch is satisfactory. In Figure l, the clearance between the cushion bushing 24 and the cylinder cover bore 22 is shown in exaggerated form at 21. When the piston has completed its stroke, there is clearance both above and below the cushion bushing as shown at 23 in Figure 3'.

In the preferred form shown in the figures, the edge of the bushing formed by the inner bore 32 and the lateral face 3,4 has been tapered or chamfered to form an 'engaging surface 36.

Referring now tothe piston structure,` a piston rod 38 is shown, part of which extends through a piston 40 so as to form a cushion nose 442. The piston rod is threaded as at 44, land the piston is secured to the rod by a nut or other suitable securing means 46. 48 indicates an O-ring seal between the piston 40 and the piston rod 38. Sealing rings indicated generally at 50, form a seal between the piston A40 and the cylinder Wall or casing 10.

A pocket or recession 52` in the piston 40 forms an air pocket or pressure chamber when the piston is in its closed position, such as shown in Figure 2.

ln order to provide the cushioning effect above described, the diameter 41 of the cushion nose 42 may be slightly smaller than the inner diameter 32 of the bushing. Again, using a 4 inch cylinder as an example, a tolerance between the cushion nose and the bushing of .0004 to .0010 inch is satisfactory. When the cushion nose 42 is in contact with the bushing 24, the bushing rests on top of the nose, with an air passage 43, as shown in Figure 3, formed between the bottom of the nose and the bushing, having so small a clearance within the bushing bore that in effect the remaining air in the cylinder is entrapped to retard the forward movement of the piston.

In the preferred form, the forward or leading edge of the cushion nose is tapered or chamfered as at 54, so as to form an engaging surface.

The use, operation and function of the invention is as follows:

tAs the piston rod and piston move forward in the cyllinder toward the cylinder cover, the air in the cylinder is forced through the intake and exhaust port 18. When the piston has moved forward to the point where the engaging surface 54 of the cushion nose contacts the engaging surface 36 of the cushion bushing, the rush of air from the cylinder through the exhaust port will be substantially stopped. As the piston continues forward the lair remaining in the cylinder will be compressed. This tends to retard or cushion the piston. This cushioning prevents damage from impact to both the piston and the cylinder cover and also provides quieter operation.

ln order to prevent damage to the cylinder, piston, cushion nose and cushion bushing due to any misalignment of the cushion nose and cushion bushing bore that may occur from manufacturing tolerances and to maintain the close tit of the cushion nose in the cushion bushing bore lan automatic alignment of the bushing with the cushion nose is provided. As the tapered or chamfered engaging surfaces of the nose and bushing meet, the bushing will be moved radially in the bore in the cylinder, so las to align itself on the cushion nose.

Whereas I have given examples of tolerances or clearances as applied to a certain size cylinder, it should be understood that the invention is not limited to the tolerances shown, or to the ratio between the tolerance and cylinder size, as these examples are purely illustrative.

My invention is meant to include all cylinders constructed in accordance with the general principles disclosed. Therefore I only wish to be limited by the following claims:

1. A self-cushioning device including a cylinder, a cylindrically apertured cylinder head, a piston and piston rod extension mounted for movement toward and from the head, a rigid metallic cylindrical cushion bushing loosely socketed in the aperture, the outer diameter of the bushing being somewhat less than the diameter of the aperture, the axial length of the bushing being somewhat less than the depth of the aperture, a packing ring interposed between the end of the bushing and the bottom of the aperture adapted to bias the bushing out of contact with such bottom, means engaging the opposite end of the bushing to hold the bushing in the aperture with the packing means engaging the bottom of the aperture.

2. In combination, a cylinder, a piston mounted for reciprocation therein, a cylinder head cylindrically apertured in opposition to and concentric with the piston, a rigid metallic internally and externally cylindrical bushing socketed in the aperture with clearance to permit radial movement of the bushing, the bushing being bounded at each end by plane surfaces, holding means engaging the surface nearest the piston to hold it in the socket, the distance between the holding means and the bottom of the aperture being greater than the axial length of the bushing, an annular compressible packing ring socketed in the opposite face of the bushing and in contact with the bottom of the aperture, yieldingly biasing the bushing toward the holding means, a cylindrical member carried by the piston adapted to penetrate and make a Working t with the bushing and center it in the aperture.

References Cited in the tile of this patent UNITED STATES PATENTS 2,493,602. Sterrett Ian. 3, 1950 2,710,595 Peterson June 14, 1955 2,804,052 Halladay Aug` 27, 1957 

